The invention relates to a wheel suspension arrangement for a vehicle having a longitudinal direction, a transverse direction and a vertical direction. The wheel suspension arrangement comprising a wheel holder for supporting a vehicle wheel, wherein a first vertical end region of the wheel holder is pivotally attached to a vehicle support structure by means of a rigid control arm, and wherein the second vertical end region of the wheel holder is attached to the vehicle support structure by means of a leaf spring. A longitudinal direction of the leaf spring is arranged substantially in the transverse direction of the vehicle. The leaf spring is pivotally attached to the vehicle support structure at a transverse centre region of the vehicle, and the leaf spring is located vertically offset from a pivotal attachment location of the leaf spring.
The invention is suitable for being applied in heavy-duty vehicles, such as trucks and buses. Although the invention will be described with respect to a truck, the invention is not restricted to this particular vehicle, but may also be used in other vehicles such as busses and automobiles.
There are many different wheel suspension arrangements available for road vehicles, such as dependent suspension arrangements having a rigid or semi-rigid beam connecting the transversally opposite wheels of a vehicle, or individual wheel suspension arrangements, such as MacPherson design and double wishbone design. The wheel suspension arrangements differs mainly in terms of how the vehicle wheels are connected to the chassis of the vehicle and the wheel suspension motion is controlled in terms of suspension motion path, suspension motion length and damping of suspension motion. Each wheel suspension arrangement is associated with certain advantages and disadvantages in terms of manufacturing cost, weight, robustness, required maintenance cost, vehicle handling, tire wear, etc. U.S. Pat. No. 2,149,895 (FIG. 3) shows a suspension design of a vehicle having as its object improvement of the effect of the springing of the vehicle.
A wheel suspension arrangement is the arrangement of springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. It is known that the double wishbone suspension design generally provides very good vehicle handling and provides many different suspension parameters for enabling configuration of the suspension arrangement according to the each specific vehicle type. The double wishbone suspension design is however generally also conceived as having a relatively high manufacturing and maintenance cost due the high complexity of the linkage and elastic mountings.
The double wishbone design also has drawbacks in terms of varying wheel camber angle upon vehicle body roll, which typically occurs during vehicle cornering. A varying camber angle is generally undesirable because this results in a camber angle that offset from a desired, optimal, camber angle during certain vehicle operating conditions. Driving a vehicle with a camber angle offset from a desired camber angle generally results in reduced vehicle handling performance and in increased tire wear.
It is desirable to provide a wheel suspension arrangement that provides low variation in camber angle during vehicle driving while avoiding costly and complex design solutions.
According to an example embodiment of the invention, the wheel suspension arrangement comprises a wheel holder for supporting a vehicle wheel, wherein a first vertical end region of the wheel holder is pivotally attached to a vehicle support structure by means of a rigid control arm, wherein a second vertical end region of the wheel holder is attached to the vehicle support structure by means of a leaf spring, wherein a longitudinal direction of the leaf spring is arranged substantially in the transverse direction of the vehicle, wherein the leaf spring is pivotally attached to the vehicle support structure at a transverse centre region of the vehicle, wherein a centre of the leaf spring is located vertically offset from a pivotal attachment location of the leaf spring, and wherein the pivotal attachment location of the leaf spring is vertically offset towards the side of the rigid control arm.
By providing the wheel holder with two vertically offset attachments to the vehicle support structure, a suspension design having wheel motion geometry similar to a double wishbone design is accomplished. However, the use of a transverse leaf spring as one linkage between the wheel holder and the vehicle support structure results in an additional functionality in terms of shock absorption due to the inherent spring constant of the leaf spring. The additional spring stiffness functionality of the leaf spring enables omission, or at least reduced capacity, of the conventional spring stiffness capacity by means of coil springs or air springs, such that a more compact and more cost-efficient design of the wheel suspension arrangement is enabled.
The leaf spring provides a slightly different wheel holder motion geometry compared with the motion geometry provided by means of a bar linkage of a conventional double wishbone suspension design. However, the difference is relatively small and the leaf spring geometry during bending can be adapted according to the linkage design of the other wheel holder linkage, such that the leaf spring can relatively accurate simulate the motion geometry of a conventional double wishbone suspension design.
Moreover, by providing the pivotal attachment location of the leaf spring vertically offset towards the side of the rigid control arm, a reduced camber variation of the wheels during vehicle body roll is accomplished, such that improved vehicle handling and reduced tire wear is accomplished during vehicle body roll.
According to some example embodiments, the leaf spring may pivotally be attached to the vehicle support structure by means of a spring holder which is rigidly connected to the leaf spring, The spring holder may be pivotally attached to the vehicle support structure around a substantially horizontal axis at the transverse centre region of the vehicle, and the leaf spring may be located vertically offset from a pivotal attachment location of the spring holder. Use of a spring holder provides a cost effective solution for accomplishing the desired pivotal connected of the leaf spring to the vehicle support structure.
According to some example embodiments, a first vertical distance between the pivotal attachment location and a control arm extension at a transverse centre of the vehicle may be less than 50% of a second vertical distance between the leaf spring and said control arm axis at the transverse centre of the vehicle, specifically the first distance may be less than 25% of the second distance, more specifically the first distance may be less than 10% of the second distance, and yet more specifically the pivotal attachment location substantially may coincide with the control arm extension at a transverse centre of the vehicle. Reduced distance between the pivotal attachment location and the control arm extension at a transverse centre of the vehicle results in decreased camber angle variation during vehicle body roll.
According to some example embodiments, the wheel suspension arrangement further may comprise body roll damper unit and/or a body roll spring unit mounted such that pivotal motion of the leaf spring around said pivotal attachment location is affected by the body roll damper unit and/or the body roll spring unit. A body roll spring unit assists the existing wheel suspension shock absorption means for improving the vehicle anti-roll behaviour. In addition or separately, the body roll damper unit can be set to provide a relatively stiff pivotal connection of the leaf spring during short duration forces, such as those occurring when driving straight on a bumpy road where each unsymmetrical bump generates a pivoting momentum of the leaf spring. Thereby, the leaf spring will remain relatively fixed in its angular pivotal position during straight driving and the wheel suspension arrangement will operate similar to a double wishbone suspension system. However, during vehicle cornering, a long term unsymmetrical force will act on the body roll damper unit such that the leaf spring will pivot around its pivotal connection for providing the desired camber compensation. Furthermore, the provision of a body roll spring unit and/or body roll damper unit uniquely for controlling the vehicle body roll motion behaviour enables improved possibility of tuning the wheel suspension arrangement, because body roll suspension and body bump suspension can be targeted individually to a higher degree.
According to some example embodiments, the body roll damper unit and/or a body roll spring unit may be connected to the vehicle support structure and to at least one of the leaf spring, the spring holder or another member that is directly or indirectly rigidly connected to the leaf spring or spring holder.
According to some example embodiments, the body roll damper unit may be a rotational damper. A rotational damper provides a compact solution.
According to some example embodiments, the first vertical end region of the wheel holder may correspond to an upper vertical end region of the wheel holder, and the second vertical end region of the wheel holder may correspond to a lower vertical end region of the wheel holder. Provision of the leaf spring at a lower position may be advantageous in terms of vehicle packing because the leaf spring requires a certain space for shock absorption.
According to some example embodiments, the first vertical end region of the wheel holder may correspond to a lower vertical end region of the wheel holder, and the second vertical end region of the wheel holder may correspond to an upper vertical end region of the wheel holder. Provision of the leaf spring at the upper vertical end region is advantageous in terms vehicle roll rigidity because the centre of roll of the vehicle support structure is located higher in this embodiment during roll motion, and the vehicle roll rigidity is a function of the vertical distance between the centre of roll and the vehicle mass centre.
According to some example embodiments, a transverse length of a Ross line of the leaf spring may correspond substantially to a transverse length of the rigid control arm measured between its inner and outer pivotal attachment locations. The transverse length of the Ross line determines the geometrical motion of the ends of the leaf spring during suspension motion of the vehicle. By selecting the transverse length of the Ross line to correspond substantially to the transverse length of the rigid control arm substantially zero, or at least very small, camber variation during vertical motion of an associated wheel is enabled. Vertical wheel motion typically occurs when driving a vehicle straight on a bumpy road.
According to some example embodiments, an inner pivotal attachment location of the rigid control arm to the vehicle support structure may be located in the same longitudinally extending vertical plane as a Ross point of the leaf spring. This suspension layout, in combination with the previously defined length of the Ross line, assists in enabling the desired substantially zero, or at least very small, camber variation during vertical motion of an associated wheel.
According to some example embodiments, an outer pivotal attachment location of the rigid control arm to the wheel holder may be located in the same longitudinally extending vertical plane as an attachment location of the leaf spring to the wheel holder. This suspension layout, in combination with the previously defined length of the Ross line, assists in enabling the desired substantially zero, or at least very small, camber variation during vertical motion of an associated wheel.
According to some example embodiments, the Ross line of the leaf spring may be parallel with a straight line extending between an inner and outer pivotal attachment location of the rigid control arm as viewed from the front of the vehicle. This suspension layout, in combination with the previously defined length of the Ross line and inner or outer pivotal attachment location, assists in enabling the desired substantially zero, or at least very small, camber variation during vertical motion of an associated wheel.
According to some example embodiments, each transverse end region of the leaf spring may be connected to an individual wheel holder. Direct connection to a wheel holder at each side of the leaf spring provides a compact and cost-efficient suspension design.
According to some example embodiments, the spring holder may be rigidly connected to the leaf spring at a single central location. The single central connection provides an equal distribution of forces on the left and right side of the leaf spring, as well as a costs-effective design.
According to some example embodiments, the spring holder may at least partly surround a portion of the leaf spring for establishing the rigid connection. This design of the rigid connection provides high robustness and reliability.
According to some example embodiments, the spring holder may clamp the leaf spring over a portion extending at least 50 millimeters in the transverse direction for establishing the rigid connection, specifically at least 75 millimeters in the transverse direction, and more specifically at least 100 millimeters in the transverse direction. The length of the clamping portion is a parameter influencing the torque level that may be transferred between spring holder and leaf spring while having a high internal angular stability between the leaf spring and spring holder. This is particularly desired when a damping unit and/or shock absorption unit is connected to the spring holder.
According to some example embodiments, the spring holder may clamp the leaf spring over a transverse portion, and a ratio between a transverse clamping portion of the spring holder to the distance between the leaf spring to the pivotal attachment location is in the range of 1:0.5-1:5, specifically 1:2-1:4. As described above, the clamping portion is a parameter influencing the torque level that may be transferred between spring holder and holder.
According to some example embodiments, the rigid control arm may comprise at least two longitudinally spaced apart pivotal connections to the vehicle support structure. The spaced apart locations provide means for transferring increased level of longitudinal stability between the wheel holder and vehicle support structure. This is particularly advantageous at suspension of a wheel that is arranged to transmit relatively high levels of longitudinal force between the vehicle support structure and wheel holder, such as during vehicle braking or acceleration.
According to some example embodiments, the rigid control arm may be manufactured to form a single entity. This result in reduced manufacturing costs compared with a multi-unit control arm. It is understood here that the wheel suspension arrangement comprises only one rigid control arm, except possibly an additional rigid steering linkage.
According to some example embodiments, the second vertical end region of the wheel holder may be attached to the vehicle support structure only by means of the leaf spring. This means that the second vertical end region of the wheel holder is free from any additional suspension control arms, except possibly an additional rigid steering linkage.
According to some example embodiments, the wheel suspension arrangement further may comprise a body suspension damper unit and/or a body suspension spring unit mounted such that vertical motion of the wheel holder is affected by the body suspension damper unit and/or the body suspension spring unit.
According to some example embodiments, the body suspension damper unit and/or a body suspension spring unit may be mounted, directly or indirectly, between the vehicle support structure and one of the rigid control arm; the wheel holder or leaf spring.
According to some example embodiments, the wheel holder may form a king post provided with a wheel spindle holder for a steerable wheel.
According to some example embodiments, the wheel holder may be provided with a wheel hub for a, driven or non-driven, non-steerable wheel.
According to some example embodiments, a vehicle comprising a wheel suspension arrangement as discussed above may be provided.
The term control arm extension herein refers to an inward extension of a straight line extending between an inner and outer pivotal attachment location of the rigid control arm as viewed from the front of the vehicle, wherein the extension extends in the same direction as the straight line.
Further advantages and advantageous features of the invention are disclosed in the following description and in the dependent claims.